Our previous findings suggested that high and low levels of infection in humans by certain strrains of S. mutans may be related to the ability of saliva to induce baterial aggregation. Such a relationship was not observed with humans with intermediate levels of infection. Further studies with more human volunteers showed a diurnal variation in saliva-induced aggregation between 10 and 30%. In one isolated case as much as a 70% variation was observed. The ability of saliva to aggregate oral streptococci appeared not to be related to the numbers of indigenous streptococci or S. mutans present in the saliva. Results of recent experiments showed that host-produced IgA, IgG, albumin, lysozyme and two thermo-stable, acidic proteins were present in human saliva adsorbed to hydroxyapatite. Preliminary results showed that preparations of IgG, IgA, and thermo-stable protein stimulted glucan synthesis by S. mutans glucosyltransferase; lysozme reduced glucan formation. The effects of these saliva-associated host proteins on bacterial aggregation, adsorption of bacteria to hydroxyapatite and on glucosyltransferase-mediated aggregation and adherence of oral streptococci are under investigation.